Field of the Invention
The present invention relates to an image pickup apparatus with an emission unit, a control method therefor, and a storage medium storing a control program therefor, and in particular, relates to emission control of a light emission device, such as a flash device that is used in an image pickup apparatus.
Description of the Related Art
In general, there are some image pickup apparatuses like digital cameras that are equipped with light emission devices like flash devices. Furthermore, there is a known system in which a light emission device is located at a position away from an image pickup apparatus and is controlled by wireless control, for example, to photograph.
Moreover, although photographing in a dark photographing scene etc. is becoming possible because an S/N characteristic of an image pickup sensor, such as a CMOS image sensor, improves, it is necessary to control an irradiating light quantity (an emission quantity) of a light emission device with sufficient accuracy.
In order to control an emission quantity with sufficient accuracy, it is required to extract correctly a main object of which brightness should be controlled properly. For example, there is a technique that performs light control by calculating a plurality of photometry outputs obtained by dividing reflected light from a field into a plurality of areas and by measuring while operating a ratio contributing to light control according to focusing information (see Japanese Laid-Open Patent Publication (Kokai) No. H4-355733 (JP H4-355733A)).
On the other hand, there is an image pickup sensor that is mounted in an image pickup apparatus and that obtains a plurality of image signals by allocating a plurality of pixels to one micro lens (ML) to separate a pupil (pupil division). Then, this kind of image pickup apparatus performs a phase difference AF control according to the image signals concerned.
In the image pickup apparatus equipped with such an image pickup sensor, the information used in the phase difference AF control can be utilized for controlling an emission quantity with sufficient accuracy at the time of photographing by emitting a light emission device (flash photographing).
For example, there is a technique that obtains distance distribution of areas in an image using a pair of image signals (i.e., a phase difference image) and that removes light distribution unevenness of the light emission using the distance distribution concerned.
Incidentally, one of photographing effects by a flash photographing is what is called “to stop a moving object”. When photographing an object with proper luminance under low illumination, short-time irradiation (an order of some tens through some hundreds of microseconds) of strong light by a light emission device stops an object, and gives an image that is free from a camera shake and an image blur.
In order to control an emission quantity with sufficient accuracy with respect to a moving object, it is necessary to extract the moving object concerned correctly. For the purpose, it is useful to use the focusing information.
However, the emission control disclosed in the above-mentioned publication needs to obtain the focusing information in addition to the photometry information for the emission control. Accordingly, when a moving object is photographed, a mismatch due to time deviation occurs between a position of the object at the time of photographing and the focusing information used for the emission control.